Can de-centered lens be fixed? Experiences?

Usually, if I discover a lens is de-centered after purchase I exchange it. However, I discovered a 18-135mm Canon (not STM) is de-centered along the top 20% of the frame at 70mm+. F8 improves the overall softness, and F11 improves the entire image, but that's quite slow for telephoto.  Too late for a return but covered by warranty. I'll spend the money to send it in for repairs if I hear a good success rate for this type of problem. De-centering seems to be a rather common problem (at least with my experiences) for d-slr lenses and even fixed lens cameras. Thanks.

Greg